Wednesday, May 04, 2011

Sahara Desert-Africa

The Sahara is the world's largest hot desert. At over 9,400,000 square kilometres, it covers most of Northern Africa, making it almost as large as Europe or the United States. The only larger desert in the world is Antarctica, classified as such because of very low precipitation rates. The Sahara stretches from the Red Sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic Ocean. To the south, it is delimited by the Sahel, a belt of semi-arid tropical savanna that comprises the northern region of central and western Sub-Saharan Africa.

The Sahara covers parts of several African nations including Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Sudan and Tunisia. Most of the Sahara Desert is undeveloped and features a varied topography. Most of its landscape has been shaped over time by wind and includes sand dunes, sand seas called ergs, barren stone plateaus, gravel plains, dry valleys and salt flats. Around 25% of the desert is sand dunes, some of which reach over 500 ft (152 m) in height.

The Sahara has one of the harshest climates in the world. The prevailing north-easterly wind often causes sand storms and dust devils. When this wind reaches the Mediterranean, it is known as sirocco and often reaches hurricane speeds in North Africa and southern Europe. Half of the Sahara receives less than 20 mm of rain per year, and the rest receives up to 100 mm per year. The rainfall happens very rarely, but when it does it is usually torrential when it occurs after long dry periods.